Spectroscopic and Biological Investigations of 4-[(1E)-N-(2-aminophenyl) ethanimidoyl]-3-methyl-1-phenyl-1H-pyrazol-5-ol and its Copper (II) Complex

This study reports the synthesis, characterization, and antimicrobial evaluation of a novel Schiff base ligand (4-[(1E)-N-(2-aminophenyl) ethanimidoyl]-3-methyl-1-phenyl-1H-pyrazol-5-ol) derived from 4-acyl pyrazolone and its copper (II) complex. The work aims to correlate the structural modifications induced by metal coordination with variations in biological activity. The experimental procedure involved the condensation of 4-acyl pyrazolone with 1,2-diaminobenzene to form the Schiff base ligand, followed by complexation with copper (II) chloride dihydrate (CuCl₂·2H₂O) to yield the corresponding Cu (II) complex. Structural elucidation was achieved using elemental analysis, molar conductivity, infrared (IR), ultraviolet–visible (UV–Vis), proton nuclear magnetic resonance (¹H NMR), and gas chromatography–mass spectrometry (GC–MS) techniques. Spectroscopic analyses confirmed the formation of the Schiff base through the characteristic azomethine (C=N) absorption at 1636 cm⠻¹ and coordination to Cu(II) via N,N,O donor sites, as evidenced by metal–ligand (M–L) bands at 667.2 cm⠻¹. The Cu(II) complex displayed a higher melting point and molar conductivity than the free ligand, indicating greater thermal stability and a non-electrolytic nature. Antimicrobial activities were assessed against Salmonella typhi, Escherichia coli, Staphylococcus aureus, Streptococcus pyogenes, and Candida albicans using the agar well diffusion method following CLSI standards. The Cu(II) complex exhibited enhanced antimicrobial efficacy compared to the free ligand, except against S.aureus. Minimum inhibitory concentration (MIC) and minimum bactericidal/fungicidal concentration (MBC/MFC) values further confirmed improved potency upon complexation. The increased activity of the Cu (II) complex is attributed to enhanced lipophilicity and cell membrane permeability in accordance with Tweedy’s chelation theory. Overall, the synthesized Cu (II) complex demonstrates promising potential for development as a broad-spectrum antibacterial and antifungal agent.